The present disclosure relates to a protection element for protecting a circuit to be protected against electrostatic discharge caused by external static electricity, and a semiconductor device including the protection element. Also, the present disclosure relates to an electronic system including the semiconductor device.
In general, in a semiconductor integrated circuit, such as a Large Scale Integration (LSI) and so on, importance is increasing in protecting a circuit to be protected against a surge current that occurs on a power line of an internal circuit (hereinafter referred to as a circuit to be protected) having a predetermined function with a trend toward smaller circuit sizes and lower voltages.
As a typical surge current that occurs on a power line, an ESD surge, which is a sharp rise in power line voltage by electrostatic discharge (ESD) on an external terminal of the power line, is widely noted.
It becomes necessary for an element or a circuit (hereinafter referred to as a protection element) that protects a circuit to be protected against an ESD surge to have a function of determining whether an input electric signal is an ESD surge or not. In such a protection element, a determination is made that if an input electric signal is an ESD surge, the input electric signal is diverted outside, and if not, the input electric signal is allowed to directly pass through the circuit to be protected.
In a Gate Grounded Metal Oxide Semiconductor (GGMOS), which is a typical protection element, the determination is made on the basis of an input voltage. For example, in the case where a circuit to be protected usually operates at 2 V, and a withstand voltage is 4 V, the GGMOS that protects the circuit to be protected is adjusted to work at input of 3 V. Thereby, for example, if the input voltage becomes 3 V or more, the GGMOS diverts the current, and thus the circuit to be protected is protected.
Also, as another typical protection element, a protection element having an RCMOS structure is provided. In the RCMOS structure, a resistor and a capacitor are connected to a CMOS-type inverter. The RCMOS is generally used for a protection element that protects a power source circuit, and determines whether an input electric signal is an ESD surge current or not by a rise time of the input pulse. In the power source circuit, a rise time of a pulse of turning on the power is long, and a rise time of an ESD surge is short. Accordingly, in the RCMOS, if the rise time of the pulse of the input electric signal is short, the input current is determined to be an ESD surge current, and the current is diverted outside, and if the rise time of the pulse of the input electric signal is long, the input current is determined to be a power source current, and the current is allowed to flow into the power source circuit.
Japanese Unexamined Patent Application Publication No. 2010-50312 has disclosed a configuration of an ESD protection circuit including a protection circuit section and a control circuit section. In this configuration, the control circuit section detects whether a voltage detected by the protection circuit section exceeds a threshold voltage X or not, and thereby a circuit to be protected is protected against an ESD surge. In Japanese Unexamined Patent Application Publication No. 2010-50312, it is possible to prevent erroneous detection of a voltage having a sharp slew rate, which occurs at the time of turning on the power, as an ESD surge by disposing a control circuit section.
However, in a configuration in which the ESD protection circuit includes a protection circuit section and a control circuit section as described above, the circuit configuration is complicated compared with a simple RCMOS, and thus the circuit area is also large.
Accordingly, for the protection element, in addition to having a function of suitably protecting a circuit to be protected, it is desirable to make the circuit area smaller.